1. Field of the Invention
The present invention relates to a discharge lamp starting device for starting a discharge lamp in which an illuminant layer is provided on the inner surface of a light-transmitting bulb, and at least one of a pair of electrodes is provided on the outer or inner surface of the bulb, and also relates to an illumination apparatus equipped with the starting device.
2. Description of the Related Art
A conventional discharge lamp starting device of this type is disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2001-160497 (see FIGS. 1, 2 and 9 and the descriptions related thereto).
In this starting device, the signal output from a booster/driver circuit for driving a switching element in a booster/chopper circuit has a frequency of approximately 100 kHz. This signal is output so that the time required for the switching loss waveform of the switching element to rise or fall will fall within the range of 30 to 200 nsec.
Further, since the switching speed of the switching element is increased to enhance the efficiency of the circuit, the peak loss of the switching element exceeds 200 W.
A description will be given of the time required for the switching loss waveform to rise or fall, and the peak loss, referring to ideal waveforms. Assuming that the switching element is a field effect transistor (FET), the drain-source (D-S) voltage waveform VDS and drain (D) current waveform ID are shown in FIG. 1A. In contrast, FIG. 1B shows the switching loss waveform L of the switching element corresponding to the D-S voltage waveform VDS and D current waveform ID. Of the switching loss waveform L, Lon represents the switching loss portion when the switching element is turned on, while Loff represents the switching loss portion when the switching element is turned off.
Further, concerning Lon, Tup-on represents the rise time, and Tdown-on represents the fall time. Similarly, concerning Loff, Tup-off represents the rise time, and Tdown-off represents the fall time. Lp represents the peak loss.
In FIG. 2, “ch1, ch2” represents the drain-source (D-S) voltage waveform VDS and drain (D) current waveform ID, respectively, of an FET 1 that forms the switching element of the booster/chopper circuit of the above-mentioned conventional discharge lamp starting device. As shown, the maximum drain-source (D-S) voltage of the FET 1 is 101 V, and the maximum drain (D) current is 3.76 A.
In FIG. 2, “M1” represents the switching loss waveform of the switching element FET 1. From the switching loss waveform M1, it can be understood that the switching loss Lp-off occurring when the switching element is turned off is 262 W (96 MHz), and the switching loss Lp-on occurring when the switching element is turned on is 220 W (43 MHz). Neither Lp-off nor Lp-on satisfies the, radiated noise standards of CISPR CLASS B for information technology equipment (ITE).
FIG. 3 illustrates measured radiated noise corresponding to the above: switching loss waveform. As is shown in FIG. 3, the field strength is 58.2 dBuV/m at 43.500 MHz (indicated by P1) corresponding to the switching loss occurring when the switching element is turned on, and 57.9 dBuV/m at 96.825 MHz (indicated by P2) corresponding to the switching loss occurring when the switching element is turned off.
Thus, the conventional discharge lamp starting device exhibits a very high radiated noise level and terminal noise level. Therefore, if this device is employed in office automation equipment, such as a copy machine, scanner or facsimile machine, the equipment will not satisfy the required electromagnetic noise standards.